Wall elements for gas turbine engine components

ABSTRACT

A wall structure for a gas turbine engine combustor has an inner wall and an outer wall defining a duct, the wall structure including an outer wall having a radial step and an inner wall overlapping the radial step, a duct being defined between the inner and outer walls for the passage of cooling air; the wall structure being characterised in that the inner wall has a local thickening opposing the radial step. The velocity of cooling air through the duct is maintained and heat transfer subsequently improved.

This invention relates to wall elements for gas turbine enginecombustors.

A typical gas turbine engine combustor includes a generally annularchamber having a plurality of fuel injectors at an upstream head end.Combustion air is provided through the head and through ports providedin the combustor walls downstream of the fuel injectors.

In order to improve the thrust and fuel consumption of gas turbineengines, i.e. the thermal efficiency, it is necessary to use highcompressor pressures and combustion temperatures. Higher compressorpressures give rise to higher compressor outlet temperatures and higherpressures in the combustion chamber.

There is, therefore, a need to provide effective cooling of thecombustion chamber walls. One cooling method which has been proposed isthe provision of a double walled combustion chamber in which the innerwall is formed of a plurality of heat resistant tiles. Cooling air isdirected into the duct between the outer walls and the tile from anaperture located midway along the tile. The flow of air bifurcates intoupstream and downstream flows which are exhausted into the combustionchamber past the upstream and downstream edges of the tile. As thedownstream flow approaches the end of the tile it is supplemented by airfrom the downstream tile before exiting to form a film over thedownstream tile. The confluence of the flow with the flow from thedownstream tile is typically at a region where the outer wall of thecombustor steps radially. The radial step changes the velocity of thecooling air flow and affects the rate of heat removal at the rear edgeof the tile which is also the location of the tile most susceptible toerosion.

According to the present invention there is provided a wall structurefor an annular gas turbine engine combustor arranged to have a generaldirection of fluid flow therethrough, the wall structure including anouter wall having a radial step and an inner wall overlapping the radialstep, a duct being defined between the inner and outer walls for thepassage of cooling air; the wall structure being characterised in thatthe inner wall has a local thickening opposing the radial step.

The outer wall may have a plurality of apertures for feeding cooling airinto the duct.

Preferably the inner wall includes a plurality of wall elements, eachwall element having a body portion aligned in use with the generaldirection of fluid flow through the combustor and a plurality ofpedestals that extend within the duct from the body portion towards theouter wall.

Preferably the body portion provides the local thickening.

The downstream end of the body portion of an upstream wall element mayoverlap the upstream end of the body portion of a downstream wallelement.

Preferably the local thickening has a contour that follows the contourof the radial step.

According to a second aspect of the invention there is provided a wallelement for use as part of an inner wall of a gas turbine enginecombustor wall structure including inner and outer walls, the inner andouter walls defining a duct therebetween, the wall element having a bodyportion aligned in use with a general direction of fluid flow throughthe combustor, the wall element having a local thickening in itsdownstream end region the local thickening being adapted to oppose aradial step in the outer wall.

Preferably the wall element has a plurality of pedestals arranged in useto extend within the duct from the body portion towards the outer wall.

Embodiments of the present invention will now be described by way ofexample only and with reference to the accompanying drawings, in which:—

FIG. 1 is a sectional side view of the upper half of a gas turbineengine;

FIG. 2 is a vertical cross-section through the combustor of the gasturbine engine shown in FIG. 1;

FIG. 3 is a diagrammatic vertical cross-section through part of the wallstructure of the combustor shown in FIG. 1.

Referring to FIG. 1, a gas turbine engine generally indicated at 10 hasa principal axis X-X. The engine 10 comprises, in axial flow series, anair intake 11, a propulsive fan 12, an intermediate pressure compressor13, a high pressure compressor 14, a combustor 15, a high pressureturbine 16, an intermediate pressure turbine 17, a low pressure turbine18 and an exhaust nozzle 19.

The gas turbine engine 10 works in a conventional manner so that airentering the intake 11 is accelerated by the fan 12 which produces twoair flows: a first air flow into the intermediate pressure compressor 13and a second air flow which provides propulsive thrust. The intermediatepressure compressor compresses the air flow directed into it beforedelivering that air to the high pressure compressor 14 where furthercompression takes place.

The compressed air exhausted from the high pressure compressor 14 isdirected into the combustor 15 where it is mixed with fuel and themixture combusted. The resultant hot combustion products then expandthrough, and thereby drive, the high, intermediate and low pressureturbines 16, 17, 18 before being exhausted through the nozzle 19 toprovide additional propulsive thrust. The high, intermediate and lowpressure turbine 16, 17, 18 respectively drive the high and intermediatepressure compressors 14 and 13, and the fan 12 by suitableinterconnecting shafts.

Referring to FIG. 2, the combustor 15 is constituted by an annularcombustion chamber 20 having radially inner and outer wall structures 21and 22 respectively. The combustion chamber 20 is secured to an enginecasing 23 by a plurality of pins 24 (only one of which is shown). Fuelis directed into the chamber 20 through a number of injector nozzles 25(only one of which is shown) located at the upstream end of thecombustion chamber 20. Fuel injector nozzles 25 are circumferentiallyspaced around the engine 10 and serve to spray fuel into air deliveredfrom the high pressure compressor 14. The resulting fuel/air mixture isthen combusted within the chamber 20.

The combustion process which takes place generates a large amount ofheat. It is therefore necessary to arrange that the inner and outer wallstructures 21 and 22 are capable of withstanding this heat.

The inner and outer wall structures 21 and 22 are generally of the sameconstruction and comprise an outer wall 27 and an inner wall 28. Theinner wall 28 is made up of a plurality of discrete wall elements in theform of tiles 29, which are all of the same general rectangularconfiguration and are positioned adjacent each other. Thecircumferentially extending edges 30,31 of adjacent tiles overlap eachother. Each tile 29 is provided with threaded studs 32 which projectthrough apertures in the outer wall 27. Nuts 34 are screwed ontothreaded studs 32 and tightened against the outer wall 27, therebysecuring the tiles 29 in place.

Both the radially outer and inner outer walls 27 of the annularcombustor have a series of radial steps that enable optimum use of thecooling air. Air which has passed through the pedestals of an upstreamtile is relatively cool and can be used for film cooling the downstreamcombustor, which must be offset to present the file face at the exitpoint of the air flow emanating from the upstream tile. The stepadditionally strengthens the combustor against buckling under flame outor surge. The upstream end of a tile 29 lies adjacent the step whilstthe downstream end of the upstream tile axially overlaps both the radialstep and the upstream end of the downstream tile.

Referring to FIG. 3, there is shown part of the inner wall structure 21showing two overlapping tiles. 29A, 29B. Each of the tiles 29A, 29Bcomprises a main body portion 36 which, in combination with the mainbody portions of each of the other tiles 22, defines the inner wall 28.A plurality of heat removal members in the form of upstandingsubstantially cylindrical pedestals 38 extend from each body member 36towards the inner wall of the combustor 27 which forms the outer wall ofthe combustor wall structure. The downstream edge region 31 of tile 29Aoverlaps the upstream edge region 30 of tile 29B.

The body member 36 and outer wall of the wall structure 27 define a duct37 that extends therebetween. Cooling air is supplied to the duct 37through an aperture 40 extending through the outer wall 27. The flowbifurcates to provide an upstream flow 42 that flows substantially inthe opposite direction to the general flow of combustion gasses throughthe combustor and a downstream flow 44 that flows generally in the samedirection as combustion gasses through the combustor.

The body member has a thermal barrier coating 64 on the surface facingthe combustion chamber 20 to provide further heat resistance.

At the downstream end of tile 29A the downstream flow mixes with theupstream flow from tile 29B and is then exhausted as a film of coolingair over the combustor facing surface of the body member 36 of tile 29B.The confluence of the flows occurs where the outer wall 27 of thecombustor wall structure steps radially.

To avoid an excessive reduction in the velocity of the air flow throughthe duct at this point the body member 36 has a circumferentiallyarranged local thickening 50 which follows the radial step of the outercold-skin wall 27. The thickening is contoured to a maxima beforereducing as it extends axially rearward. This enables a relativelyconstant velocity across the whole length of the duct 37 therebymaintaining a relatively high heat removal rate, which drops if thevelocity of cooling air flow drops significantly. The high heat removalis therefore maintained particularly at the downstream edge region of atile where the tile temperature peaks and the tile integrity is atgreatest risk.

Pedestals 38 are provided on the region of local thickening 50. Thelength of the pedestals is maintained over the hump shaped localthickening maintaining the high heat removal afforded by thesestructures. The pedestals define a flow-path for the supplemental airfrom the downstream tile and which maximises the volume flow of coolingair within the pedestal array.

Various modifications may be made without departing from the scope ofthe invention. For example, the degree of axial overlap of the upstreamand downstream tiles may be varied to optimise the film of air over thedownstream tile. Similarly, the pedestal length in the region of thehump could be adjusted to optimise heat removal and the shape of thehump/local thickening could be refined to maintain the optimum coolingair velocity.

1. A wall structure for an annular gas turbine engine combustor arrangedto have a general direction of fluid flow therethrough, the wallstructure including an outer wall having a radial step and an inner walloverlapping the radial step, a duct being defined between the inner andouter walls for the passage of cooling air; the wall structure beingcharacterised in that the inner wall has a local thickening opposing theradial step and a plurality of pedestals extending from the localthickening towards the outer wall.
 2. A wall structure according toclaim 1, wherein the outer wall has a plurality of apertures for feedingcooling air into the duct.
 3. A wall structure according to claim 1,wherein the inner wall includes a plurality of wall elements, each wallelement having a body portion aligned in use with the general directionof fluid flow through the combustor and a plurality of pedestals thatextend within the duct from the body portion towards the outer wall. 4.A wall structure according to claim 3, wherein the body portion providesthe local thickening.
 5. A wall structure according to claim 3, whereinthe downstream end of the body portion of an upstream wall elementoverlaps the upstream end of the body portion of a downstream wallelement.
 6. A wall structure according to claim 1, wherein the localthickening has a contour that follows the contour of the radial step. 7.A wall element for use as part of an inner wall of a gas turbine enginecombustor wall structure including inner and outer walls, the inner andouter walls defining a duct therebetween, the wall element having a bodyportion aligned in use with a general direction of fluid flow throughthe combustor, the wall element having a local thickening in itsdownstream end region the local thickening being adapted to oppose aradial step in the outer wall and having a plurality of pedestalsarranged in use to extend within the duct from the body portion towardsthe outer wall.